How many people groups need Bible translations—and especially, how many frontier people groups?
This data is available on Joshua Project. For various reasons, the list isn't absolutely perfect: the question of 'how do we determine if a people group needs a translation' is a complex one that translators and their organizations are still grappling with. Nevertheless, for a global picture, a 'good enough' answer can be obtained and graphed.
I used Joshua Project’s "Definite Need" filter, and then aggregated by my Stage of % Christian levels based on the % Christian of the group. The results:
Stages: 0, <0.1% Christian; 1, 0.1% to 2%; 2, 2%to 8%; 3, 8% to 32%; 4, 32% to 90%; 5, 90% and higher. Stage 0 = Frontier; Stage 0+1+ "part of 2" = Unreached.
That 'definite translation need' at Stage 5 (>90% Christian) surprised me. But some hint as to the reason can be seen in the two graphs: there is a high count of groups, but a low population figure; this means that we're dealing with a lot of tiny groups. And if you look at the data set on the website, that's what you'll see.
If you have an interest in this subject, I suggest going and playing around with the filters and examining this aspect of the remaining task.